A number of important human parasitic diseases are transmitted by insect vectors. Organisms that cause diseases such as malaria or filariasis must evade or defeat the defensive responses of their insect vectors if successful transmission to human hosts is to take place. However, the cellular and molecular interactions between insects and such parasitic organisms are not well understood. In comparison with our detailed knowledge of the vertebrate immune system, the molecular mechanisms of insect immune responses remain largely a mystery. The primary response of insects to eukaryotic parasites is encapsulation of the invading organism by the host insect's hemocytes. The long term objective of this project is to identify and characterize proteins from insect hemocytes that are involved in the encapsulation process. We will approach this problem with the use of a unique panel of monoclonal antibodies to hemocytes of Manduca sexta that we have generated. The specific aims are: 1) Identification of molecules within the vesicles of granular hemocytes or on the surface of plasmatocytes and granular hemocytes that are involved in hemocyte adhesion and encapsulation. We will screen our panel of monoclonal antibodies to find those that can disrupt plasmatocyte spreading, hemocyte adhesion, or encapsulation in in vitro assays. 2) Characterization of molecules identified in Aim 1. We will use the monoclonal antibodies that disrupt hemocyte responses as reagents to determine the size of the corresponding antigen, to purify the corresponding antigens, and to clone cDNAs for the corresponding antigens from hemocyte libraries. We will determine the sequences of the cDNAs and analyze the deduced amino acid sequences of the hemocyte proteins. The identification of proteins that function in hemocyte encapsulation is a first step toward understanding how they function and eventually toward understanding how parasites avoid the encapsulation response in insect vectors of human diseases.